PI Tagging Shellfish

We are investigating the use of PIT tags to tag Pacific razor clams (Siliqua patula) for a growth study. So far we have had minimal success injecting the tag into the soft tissue of the animal. We have had more success attaching the tag to the exterior of the shell using glue. Can anyone share experiences using PIT tags in any shellfish specie? Dan Ayres Wash Dept of Fish and Wildlife